Switching mechanism



Sept. 3, 1940. J. T. CARLSON SWITCHING MECHANISM Filed July 2l, 1937 INVENTOR JOHN TGAP/ 50N BY Q Q /7 l V ATTORNEY RM THERMDSTAT Patented Sept. 3, 1940 PATENT OFFICE SWITCHING MECHANISM John T. Carlson,

Master Ohio Dayton, Ohio, assignor to The Electric Company, a corporation of Application July 21, 1937, Serial No. 154,907

12 Claims.

This invention relates to an improved switching mechanism and more specifically is directed to a. thermostatically controlled switching device.

An object of this invention is the provision of a switching mechanism embodying certain improvements and advantages over those now known in the prior art.

Another object of this invention is the provision of an improved thermostatically controlled switching device.

Stili another object of this invention isithe combination of a switching device controlled by a bi-inetallic thermostatic element, said switching device being so constructed and arranged that movement of the switch beyond its contact making position imposes no strain upon the bimetallic element.

A fourth object of this invention is the construction of a thermostatically actuated switch mechanism inwhich the switch actuating device is permitted to rotate beyond the normal switch contacting position without imposing any substantial further strain upon the thermostatic actuating element.

A more speciiic object of this invention is the provision of an improved thermostatically actuated stack control switch.

With these and incidental objects in view, the invention consists in certain novel features in construction and combination of parts which are set forth in the appended claims and a preerred form of embodiment whereof is hereinafter described with reference to the drawing which accompanies and forms part of the speciiication, wherein:

Fig. 1 is a longitudinal view, partly in crosssection, of my combined switch mechanism and the actuating device therefor;

Fig. 2 is a front View of the switch mechanism, partially cut away; and

Fig. 3 is a diagrammatic view of a system embodying my improved switch device.

Referring to Figs. 1 and 2 showing a preferred form in which my switching device can be constructed, a thermostatic element such as a bimetallic member I in the form of a helix is mounted within a stackwell I2. This thermostatic element may be, by way of illustration, mounted within the stack (not shown) of a furnace to be controlled in one or more of several known ways.

The stackwell I2 is preferably provided with an inwardly projecting annular groove I4 adapted, for the purposes of mounting the stackwell, to lit into an annular recess I6 of a ring I8 of a (Cl. D-138) stack tube 20. One end of the thermostatic member is adapted to be connected to a projecting portion 22 of the stack tube 20 by suitable means such as a screw 24. The other end of the bi-metallic element is operatively attached to 5 one end of the actuating rod 26 in any desirable manner, illustrated in this case as by a rivet 28. The stack tube is held in position by means of a plate collar 30 and set screw 32 attached to a mounting plate 34 which, in turn, through holes 10 36 therein, may be fastened in any desired manner to the stack to be controlled.

The switch shown generally at 40 is built up from a flanged casing 42 having an inner backing of insulation shown at 44. A sub-base 4B for 15 the switching elements is attached to the flanged portion of the casing, as for example, by screws 48. A switch lever bearing mounted upon the actuating shaft 26 serves as the support for the switch arms 52 and 54 and by means of 20 washers 56 and 58 holds them in a rm but rotatable manner. The switch arms 52 and 54 are adapted to be turned about the bearing 50 for purposes hereinafter described.

In order to transmit the motion imparted by 25 the thermostatic element I0 to the driving shaft 25, a roller cam 60 is attached at the other end of this shaft. The said cam 60 has a small wheel t2 journaled thereon, and is fastened against relative rotation to the shaft 26 in any suitable 30 manner, illustrated in the present embodiment of this invention as by means of cooperating bolt 54, lock washer B6, and nut 68. Upon rotation of the roller cam, it is adapted to engage the spring aiin connected in turn to the switch lever 'l2 as at 74. The members lll and l2 are mounted in any suitable manner for movement relative to the switch arm 54 shown, by way of example only, as pivoted about a stud on this arm. A spring member I6 is attached to the switch arm 'l2 as at 'I8 and is u sed to bias the switch arm through its springing reaction against the stop member 80. The switch lever 'I2 forms electrical Contact with either one or the other of contacts 82 or 84 mounted upon an 45 insulating base 86 which, in turn, is attached to the main switch arm 54. In order to indicate the position at which the roller cam will actuate the switch lever or, in other words, the setting of the switch, the switch arm 54 has a 50 pointer 88 projecting through an opening in the face of the switch cover 90 and cooperating with suitable indicia shown at 94 as imprinted or otherwise placed thereon.

The other switch arm 52 has a spring actuat- 55 ing member 'Il with which the roller cam is adapted to cooperate and indicating pointer 89, and in all other respects is similar to arm 54.

For mounting the switch casing on the stack tube 20, means such as a back plate 96 may be used. A flexible conduit 98 is a convenient manner for conducting the electrical lead wires such as |00, |02, |04, and |06, to the switch contacts. In order to clearly describe the operation of my improved thermostatic switch, it has been illustrated, by way of example, in a stack control system diagrammatically shown in Fig. 3. From a suitable source of power (indicated, but not shown) current is preferably drawn through a transformer ||0. A conductor 2 connected to one side of the transformer leads, in turn, to a neutral terminal ||4 of the furnace control. Since the specific form of means for controlling the furnace, whether it be by controlling the drafts, blowers, dampers, or any other part thereof, is immaterial for the purpose of illustrating this invention, this control has merely been indicated. From the other side of the transformer I I0, a conductor ||6 is connected through a terminal B of a terminal block (not shown) to the switch 12. A

From ano-ther contact on the furnace control, a circuit is completed to switch contact 85 through conductor ||8, terminal A, and conductors ||9 and |20. Another circuit from the same furnace control terminal ||1 is completed to the switch contact |22 of a room thermostat |24 through conductor I8, terminal A, and conductors ||9 and |2|` From a third terminal |26 on the furnace control the conductor |06 completes a circuit to contact 83 of the switch arm 52 and the conductor |00 completes the circuit to the contact 84 of the switch arm 56 through terminal C. A wire |28 through terminal C interconnects the switch lever 13 with the contact |29 of the room thermostat |26. The latter, in turn, is connected by conductor |02 through terminal B' to the switch contact 82 of the switch arm 56.

As shown in Fig. 3, all parts are in their neutral or normal positions, the switch arms 12 and 13 being biased against the contacts 82 and 83, respectively, and the room thermostat to the off position.

If the temperature of the room falls and more heat is therefore desired, the switch arm |25 of the room thermostat |26 will make contact with point |22. A circuit is then completed which may be traced from the terminal ||4 of the furnace control through conductor I2, transformer H0, conductor ||6, terminal B, switch lever 12, contact 82, terminal B', conductor |02, room thermostat |24 with its arm |25 and contact |22, conductors |2| and 9, terminal A, and conductor ||8 to terminal ||1 of the furnace control. This will accordingly energize the ON" position of the stack control. No circuit will be established through the conductor |20 and switch contact 85 as the switch lever 13 is biased away from this latter contact. Assuming that the stack thermostat also calls for the ON position of the furnace control, the resulting circuits will not be altered or interrupted but the stack control will remain in its ON position.

If, however, the heat within the stack becomes too great, even though the room thermostat may be in the ON position, when the switch lever 12 is moved to contact point 84, the circuit through the room thermostat will be interrupted and the furnace control will be turned to the "OFF position through the circuit now established from terminal H4, conductor H2, transformer ||0, conductor H6, terminal B, switch lever 12, contact 84, terminal C, conductor |00, back to terminal |26.

Reversely, if the room temperature rises so that the switch arm |25 of the 4thermostat |26 moves to the contact |29, a circuit will then be established from neutral terminal ||4 of the furnace control, conductor ||2, transformer ||0, conductor ||6, terminal B, switch lever 12, contact 82, terminal B', conductor |02, switch lever |25, contact |29, conductor |28, terminal C', switch lever 13, contact 83, and conductor |06, to the OFF" terminal |26 of the furnace control. But again the stack thermostat has the power to countermand the order of the room thermostat. If the stack temperature is Atoo low, indicating that there is danger of the re going out, the switch lever 13 will then move over to establish contact with the point 85. This not only interrupts the circuit to the OFF" terminal |26 of the furnace control but establishes another circuit which may be traced from the terminal H4 through conductor ||2, transformer ||0, conductor H6, terminal B, switch lever 12, contact 82, terminal B', conductor |02, switch lever |25, contact |29, conductor |28, terminal C', switch lever 13, contact 85, terminal A', conductors |20 and H9, terminal A, and conductor ||8 to the ON terminal ||1 of the furnace control. It will thus be seen that in the system described, While both theroom thermostat and the stack thermostat are able to eiect the desired stack control, nevertheless it is always the stack thermostat which has the final authority.

The purpose of such a system is that it is at all times desirable, no matter what the room temperature thermostat may wish, both to prevent overheating of the flue and to prevent the lires from going out altogether.

My improved type of thermostatic switch, while capable of many uses, is admirably adapted to operate in the foregoing system. Upon a slight variation in stack temperature, the thermostatic element I0 will either contract or expand to rotate the shaft 26 and with it the roller cam 60. This cam, in engaging either of the arms 10 or 1|, will accordingly actuate the corresponding switch mechanism. In the usual case however, the thermostatic element tends, because of an excess increase or decrease in temperature, to turn further than necessary for the desired actuation of the switch. In many switches heretofore known in the art when, by way of example, some switch actuating mechanism, such as applicants roller cam 60, acts to operate the switch mechanism, it comes against an abutment in one form or another and can turn no further. Because of this, due to the tendency of the thermostatic element .to expand or contract further, strains are imposed thereon which in a short time give such a thermostatic element a permanent set, thereby ruining its accuracy in operation. However, by designing the arms 10 and 1|, with which the roller cam comes in Contact in my improved switch, to have, upon bending, an arc substantially equal to the radius of the roller cam, the latter may then turn Within comparatively large limits Without any increase in opposing resistance and, as a result, without placing any strain whatsoever upon the actuating thermostatic element. In other Words, after the switch arm 10 or 1| has been initially moved to actuate the electrical contacts, there is provided a dwell amasar which therefore permits the further unobstructed movement of the roller cam. The position of the switch arm 13 and the roller cam 60 have been shown, by way of example, in an extreme position in dotted lines in Fig. 3. The arcuate shape which the member 10 takes after its initial movement is clearly shown in this illustration.

Because of the advantageous arrangement of the parts, this type of switch also permits easy adjustment so that the limits of high a-nd low temperatures at which the switch is adapted to operate may readily be varied. All of the switch parts are mounted on rotatable levers 52 and 54, the position of which are indicated by pointers 89 and 88 cooperating with a proper scale. Movement of these levers varies the amount of relative movement necessary before the roller cam engages the arms 1| and 10 and thus the effective temperature at which the furnace coutrol will operate. By means of the illustrated construction, variation may be made in both the high and low ends of the scale. Furthermore, no matter in what position the levers 52 and 54 may be placed, there can be no strain onthe thermostat, as the arms 'li and 10 will, after initial movement, always assume a position to allow further free travel of the roller cam. It is to be noted that while I have shown and described the arms 10 and 1I as made separately from the respective switch levers 12 and 13, these could, of course, be each made as a single piece of spring metal connected in a suitable manner to the respective switch arms 54 and 52` It will be obvious to any one skilled in the art that my invention is not limited to the specific embodiment dsclosed nor is it of any importance or signiiicance in what type of system such a switch can be used. While I have, for the sake of illustration, disclosed a bi-metallic thermostatic element in the form of a helix, it is clear that this invention is applicable to a switch actuated by an element of any other conguration. The particular manner of mounting the various parts, the type of casing, and the details of construction may all be `varied without departing from the scope of this invention andsuch scope is not limited except as defined in the following claims.

I claim:

-1. In a thermostatic switch, loi-metallic element, a drive in combination, a shaft, means for 4holding one end of said bi-metallic element against rotation and means for attaching the other end thereof to said drive shaft, a contact arm mounted for pivotal movement and having an integral curved extension, contact points adapted to cooperate with said contact arm to commutate a circuit, and means fixed to the other end of said drive shaft for engaging the curved extension of said contact arm and thereby actuating the latter.

2. The combination according to claim 1 wherein the. radius of curvature of said curved arm extension is equal to the outer radius oi rotation of said last means.

3. 'I'he combination according to claim 1 in combination with means concentric with said drive shaft for varying the engagement of said actuating means with said curved arm extension.

4. The combination according to claim 1 in which said loi-metallic element is concentric with said drive shaft.

In a switch, a drive shaft, a pair of switch arms rotatably mounted concentric to said drive shaft, a contact arm and at least one cooperating contact mounted on each of said switch arms, an extension on each of said contact arms, and means mounted on said drive shaft for engaging one or the other of said extensions for actuating one or the other of said switch arms, whereby upon rotation of said switch arms the engagement of said actuating means with the contact arms may be varied.

6. The combination according to claim 5 in which said actuating means includes a roller cam.

7. The combination according to claim 5 in which the engaging portions of said extensions are curved concentrically with the drive shaft.

8.'The combination according to claim 5 in which said actuating means includes a roller has a radius of curvature equal to the outer radius of rotation of said roller cam.

9. The combination according to claim 5 including means for biasing each of said contact arms in a direction to oppose movement thereof by said actuating means.

10. The combination according to claim 5 in combination with thermo-responsive means for actuating said drive shaft.

11. In a thermostatic switch, in combination, a bi-metallic element, a drive shaft, means for holding one end of said bi-metallic element against rotation and means for attaching the other end thereof to said drive shaft, a contact arm having a curved extension, contact points adapted to cooperate with said contact arm to commutate a circuit, and means fixed to the other end of said drive shaft for engaging the curved extension of said contact arm for actuating the latter, the radius of curvature of said curved arm extension being equal to the outer radius of rotation of said last means.

12. In a switch, a base member having a contact, a contact arm mounted on said base memcam, and the engaging portion of said extension with said contact, said contact arm including an arcuate portion of substantially constant radius. a pivotally mounted actuating arm for engaging the arcuate portion of said contact arm and moving the latter into engagement with said contact, said actuating arm having substantially the same pivotal radius as said arcuate portion, whereby. after initial engagement with said arcuate portion, said contacting arm may continue its movement without resistance while maintaining engagement of said contact arm and contact, and means for pivoting said base member about the pivotal axis of said actuating arm, whereby the initial engagement of said actuating member and arcuate portion may be varied.

JOHN T. CARLSON'. 

